WASHINGTON (Reuters) - Levels of a powerful greenhouse gas are four times as high as previously thought, according to new measurements released on Thursday.

New analytical techniques show that about 5,400 metric tons of nitrogen trifluoride are in the atmosphere, with amounts increasing by about 11 percent per year.

Ray Weiss of the Scripps Institution of Oceanography in La Jolla, California, and colleagues said it had not been possible to accurately measure this gas before.

They said nitrogen trifluoride is 17,000 times more effective at warming the atmosphere than an equal mass of carbon dioxide, although it does not yet contribute much to global warming.

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Previous estimates had put levels of the gas at less than 1,200 metric tons in 2006.

Nitrogen trifluoride, a colorless, odorless, nonflammable gas, is used to etch silicon wafers and in some lasers.

Writing in Geophysical Research Letters, Weiss and colleagues said they analyzed air samples gathered over the past 30 years under the NASA-funded Advanced Global Atmospheric Gases Experiment.

Weiss said nitrogen trifluoride needs to be regulated, as carbon dioxide is.

"From a climate perspective, there is a need to add nitrogen trifluoride to the suite of greenhouse gases whose production is inventoried and whose emissions are regulated under the Kyoto Protocol, thus providing meaningful incentives for its wise use," he said.

Michael Prather, an atmospheric chemist at the University of California at Irvine, noted nitrogen trifluoride is being used more commonly and predicted that more would be found in the atmosphere.

"It is now shown to be an important greenhouse gas," Prather, who was not involved with the Scripps study, said in a statement. "Now we need to get hard numbers on how much is flowing through the system, from production to disposal."